1. Field
An organometallic complex, an organic electroluminescent device, and a display device using the same are disclosed.
2. Description of the Related Art
An organic electroluminescent device is a display element that actively emits light when a current flows into a fluorescent or phosphorescent organic compound thin layer (hereinafter, an organic layer) in such a way that electrons and holes are combined in the organic layer. The organic electroluminescent device usually has light weight, consists of simple parts, has a simple structure for manufacturing, and secures high image quality and a wide viewing angle. In addition, the organic electroluminescent device may perfectly realize high color purity and a motion picture, and has appropriate electrical characteristics of low power consumption and low voltage driving for a portable electronic device.
In general, the organic electroluminescent device includes an anode disposed on a substrate, and a hole transport layer (“HTL”), an emission layer, an electron transport layer (“ETL”), and a cathode sequentially formed on the anode. Herein, the hole transport layer (“HTL”), the emission layer, and the electron transport layer (“ETL”) are organic layers formed of an organic compound. The organic electroluminescent device is operated as follows. When a voltage is applied between the anode and the cathode, holes injected from the anode pass through the hole transport layer (“HTL”) and move toward the emission layer. On the other hand, electrons pass through the electron transport layer (“ETL”) from the cathode and are injected into the emission layer, in which the carriers are recombined and produce exitons. The exitons are radioactively decayed and emit light with a wavelength corresponding to the band gap of a used material.
The emission layer may be formed of a phosphor material using singlet exitons and a phosphorescent material using triplet exitons depending on a light emitting mechanism thereof. The phosphor material or phosphorescent material itself doped on an appropriate host material may be used to form the emission layer. When electrons are excited, singlet and triplet exitons are formed on the host material. Herein, the singlet and triplet exitons are produced in a ratio of about 1:3.
When the phosphor material is used as an emission layer-forming material, an organic electroluminescent device wastes triplet exitons produced from a host material. However, when the phosphorescent material is used as the emission layer-forming material, both singlet and triplet exitons may be used to reach 100% internal quantum efficiency. Accordingly, the phosphorescent material may have higher luminous efficiency than the phosphor material.
On the other hand, when a heavy metal such as Ir, Pt, Rh, and Pd is introduced into an organic molecule, the singlet and triplet exitons are spin-orbitally coupled and mixed due to heavy atom effects, and are thus transferred and effectively become phosphorescent even at room temperature.
As mentioned above, various materials using a transition element compound including a transition element such as iridium, platinum, and the like have been reported as a phosphorescent light emitting material with high efficiency. However, a more highly-efficient phosphorescent material for a full color display element still needs to be developed.